1. Field of the Invention
This invention relates generally to a torsional unloading device for reducing the operating friction within an automotive suspension strut.
2. Disclosure Information
Automotive suspension designs incorporating telescoping struts have taken a variety of forms. In the classical MacPherson design, the strut is positioned between a wheel carrier, to which it is rigidly mounted, and the vehicle's chassis, to which the telescoping strut is either pivotally or resiliently mounted. A spring device is commonly mounted concentrically about the strut. This spring device may comprise either a coil spring or an air spring or some other type of spring.
In the "modified" MacPherson design, a spring mechanism is mounted between a lower control arm attached to the wheel carrier, and the chassis. With both the classic and modified MacPherson designs, the strut is rigidly fastened at its lower end to the wheel carrier and pivotally or resiliently mounted to the chassis at its upper end. The rigid mounting between the strut and the wheel carrier causes the wheel carrier to impose a bending moment upon the strut which moment is counteracted within the strut by the strut's piston and bearing. This preloading is undesirable inasmuch as the static friction resulting therefrom increases the force necessary to initiate sliding of the piston within the strut and therefore correspondingly increases the shock loading transmitted to the chassis of the vehicle when an obstruction is encountered on a roadway surface. Attempts to minimize this undesirable static friction have resulted in configurations wherein the spring or other load bearing device is eccentrically mounted about the strut, or in other configurations in which the spring mounting pads are canted at an angle to the strut's center line. Although these solutions will normally cause a reduction of strut friction, an undesirable side effect may arise inasmuch as the packaging volume of the strut assembly may increase with either of the aforementioned structures.
U.S. Pat. No. 2,992,015 discloses a suspension arrangement in which friction is said to be reduced by rearranging the geometry of a strut type suspension system such that the point of intersection of the longitudinal axes of the strut and a control arm is relocated to a point above the center of ground contact of the tire and road wheel assembly. This system may not be workable in certain vehicles because the space limitations inherent in the particular design of the vehicle.
German Offenlegungsschrift No. 1,405,372 discloses a complicated system in which strut friction is minimized through the use of a series of rollers which act upon the strut rod. This system would be excessively costly and difficult to construct.
U.S. Pat. No. 4,615,537, which is assigned to the assignee of the present invention discloses yet another system for minimizing friction within the strut through the use of an upper mounting system which preloads the strut in the opposite direction from the loads imposed by the wheel carrier. This system may, however, produce undesirable loads in the vehicle's body or chassis.
It is an object of the present invention to provide a means for reducing the operational friction of a telescoping strut without causing an increase of the strut's package volume.
It is another object of the present invention to provide a means for reducing the operational friction of a telescoping strut which is economical to produce.
It is another object of the present invention to provide a means for reducing the operational friction of a telescoping strut which produces a reduction in friction throughout the full stroke of the strut from the full jounce to the full rebound position.
Other objects, features and advantages of the present invention will become apparent with the following description of this invention.